Issue 23, 2010

Ammonia absorption in calcium graphite intercalation compound: in situneutron diffraction, Raman spectroscopy and magnetization

Abstract

The structure and superconducting properties of ammoniated calciumgraphite intercalation compound (Ca-GIC) have been investigated using in situ time-of-flight neutron diffraction, Raman spectroscopy and magnetization studies. Ammonia absorption has been carried out by exposing preformed Ca-GIC to ammonia vapour at various pressures. Our in situ neutron diffraction data reveal a complex ammonia pressure dependent structural transformation, in which the growth of secondary ammoniated Ca-GIC phases are observed at the expense of the pristine CaC6 and graphite. The ammonia absorption is irreversible in nature, and degassing the sample at elevated temperature leads to the formation of calcium amide and hydrogen. The Raman spectroscopy and magnetization studies show that the ammonia absorption not only leads to a large stacking disorder, but it also reduces the superconducting CaC6 phase fraction. Finally, we propose a molecular stacking model which accounts for the observed ammonia absorption and concomitant structural phase transitions.

Graphical abstract: Ammonia absorption in calcium graphite intercalation compound: in situ neutron diffraction, Raman spectroscopy and magnetization

Article information

Article type
Paper
Submitted
03 Sep 2009
Accepted
11 Feb 2010
First published
30 Apr 2010

Phys. Chem. Chem. Phys., 2010,12, 6253-6259

Ammonia absorption in calcium graphite intercalation compound: in situ neutron diffraction, Raman spectroscopy and magnetization

G. Srinivas, A. Lovell, N. T. Skipper, S. M. Bennington, Z. Kurban and R. I. Smith, Phys. Chem. Chem. Phys., 2010, 12, 6253 DOI: 10.1039/B917992E

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